Along with the advance in technological development of the semiconductor industry, semiconductor manufacturing technology has entered into the nano-era, which means millions of transistors and interconnecting wires need to be formed on a chip within a few square centimeters when manufacturing a very large scale integrated (VLSI) circuit chip. Accordingly, techniques for forming multi-metal layer structures have been developed to internally interconnect transistors and support elements. Chemical mechanical polishing (CMP) is a technique widely used for planarization the surface of semiconductor wafers, which is important for forming the multi-metal layer structures.
In 1984, IBM introduced CMP into the field of semiconductor manufacturing. CMP was firstly applied to planarization of inter-metal dielectric (IMD) layers in backend processes. With the improvement of devices and semiconductor processes, CMP has been applied to planarize tungsten, shallow trench isolation (STI) and copper. CMP has become a fast-growing and valuable process for IC fabrication in recent years.
The basic principle of CMP is to apply a mechanical force from abrasives in the polishing slurry towards a surface of a material to be polished, thereby generating a motive power leading to corrosion cracking in a thin layer surface with which chemical substance in the polishing slurry reacts to improve removal rate. Specifically, when a metal material is polished, the chemical substance reacts with the metal material, so that metal oxide is formed. Then the metal oxide is removed in an action of the mechanical force, so that a flat surface is obtained.
However, a large quantity of polishing byproducts including metal ions (e.g. Cu+ or Cu2+) are produced in the polishing process. This issue is particularly serious during the polishing process with a high removal rate, that is, for example, polishing copper for a top metal layer or a TSV structure of 3D packaging. The high removal rate of the metal material can cause large concentration of the polishing byproducts which may reduce the removal rate, impact the stability of the removal rate and increase defects on the metal material. Therefore, there is a need for reducing or removing the byproducts in the polishing process for metal.
FIG. 1 is a schematic top view illustrating a conventional technique for removing polishing byproducts. As shown in FIG. 1, a wafer 101 is polished on a polishing pad 103 that is disposed on a rotating polishing platen 100 (shown in FIG. 2). As described above, when the metal material on a surface of the wafer 101 is being polished with a polishing slurry, a large quantity of polishing byproducts 102 (only one of the byproducts is labeled in FIG. 1) that include metal ions are formed. During the polishing process, the polishing platen keeps rotating, so some of the polishing byproducts 102 are removed with the polishing slurry by the centrifugal force of the polishing pad. In subsequent steps (in which the wafer 101 is removed from the polishing pad 103), the polishing platen is still rotating when the polishing pad 103 arranged thereon is rinsed with deionized water or chemical cleaning solution, so some of the polishing byproducts 102 are removed with the deionized water or chemical cleaning solution in the action of the centrifugal forces.
FIG. 2 is a schematic front view illustrating a conventional technique for removing the polishing byproducts. As shown in FIG. 2, the wafer 101 is secured on a polishing head 104 by means of vacuum and pressed on the polishing pad 103 that is disposed on the polishing platen 100. The polishing platen is rotated by a rotatable axis 105 and the polishing head 104 is also rotatable relative to the polishing platen to provide a polishing motion. The polishing byproducts 102 are removed together with the polishing slurry, the deionized water or the chemical cleaning solution in the action of the centrifugal forces. However, the removal rate of the polishing byproducts is unacceptable in the prior art, especially in a polishing process which includes a relatively long polishing time period or a metal layer that has relatively large thickness.
US Patent Publication No. 20010031558A1 discloses methods for removing polishing byproducts in a CMP process for aluminum so as to reduce scratches which are formed on the wafer. However, this disclosure only partially solves the above described problems.
Therefore, there is a need to have a method and apparatus for removing the polishing byproducts with an acceptable removal rate.